feat!: remove legacy transport descriptor config

[lanycrost]

Summary

• add a conventional breaking-change commit so Release Please can publish the already-merged typed-only transport descriptor change
• no source files changed in this PR

Verification

• empty commit only; previous implementation PR Add typed-only transport descriptor config #25 passed generated bindings, Go tests, and Go lint
• buf-breaking failure in Add typed-only transport descriptor config #25 was the intentional TransportDescriptor.config field 4 removal/reservation

After this merges, Release Please should detect the breaking feature commit and open/publish the next tractatus release through the normal workflow.